In industries where hot metals are transported, stored, or refined, deep-walled refractory bodies such as furnaces, storage vessels and ladles are used to hold hot molten metal during processing. The contact of the hot metal with the refractory body causes, without protection of the contact surfaces, a rapid deterioration, corrosion, and eventually destruction of the body.
In order to prolong the useful life of a refractory body, it is usual in the metal fabrication field to spray a suitable refractory material onto the interior surfaces of the body to coat those surfaces, the refractory material being designed to insulate said surfaces from hot molten metal. The refractory material is commonly dried and powdered, and may be mixed with a suitable wetting agent, such as water, to facilitate spraying. The treatment of a refractory body with such material only protects the body for a finite length of time; therefore, regular applications of the material are required to insure protection of the interior surfaces of the body.
Because of the expense involved in repeated applications, it is essential to maximize the period over which an application of refractory material will provide protection for the refractory body. To insure maximum duration between refractory applications it is critical that the refractory material be applied evenly over the interior of the body. Any lumping or uneven application of the material will render it susceptible to chipping or faulting. Unfortunately, when the material chips, a large portion is often carried away, exposing a section of the interior surface of the body to the hot molten metal. Thus, it is desirable not only to initially apply the refractory material evenly, but also to have the option of applying the material in a manner that permits application at such resulting fault points for repair purposes. In this way, any chipping or faulting may be repaired before it causes too much damage.
The most common method of spraying refractory material is by the use of hand-held apparatus. In order to effectuate the spraying process an operator must actually enter the vessel. With such apparatus, however, this method has the disadvantage of requiring a long period of time for the vessel to cool to a safe temperature, which cooling time is unproductive, costly, and undesirable for the industry. Moreover, vessels that are used to transport molten metal in the mill are usually transported with overhead cranes; a certain amount of crane time is required to move the vessel to a remote spot where it can cool before it is sprayed. Since crane time is expensive, it is undesirable to spray vessels in such remote locations. Therefore, there is a need for an apparatus that can spray vessels while they are at or near their operating position, and while they are still hot.
The devices disclosed in U.S. Pat. No. 3,797,745, issued to Haus on Mar. 19, 1974 (hereinafter "Haus"), and in U.S. Pat. No. 3,799,445, issued to Marino on Mar. 26, 1974 (hereinafter "Marino"), purportedly eliminate some of the problems associated with hand spraying. The apparatus disclosed in Marino is particularly suitable for spraying large stationary bodies (col. 1, 11. 5-15), such as furnaces, but is not designed for smaller deep-walled vessels.
The apparatus disclosed in the Haus patent is suitable for spraying smaller refractory bodies. It utilizes a fixed upper element and a rotating bottom element, to which rotating element are attached two fixed, diametrically opposed outwardly-projecting spray nozzles. The fixed nozzles are used to coat the interior sides of the body by simultaneous delivery of refractory spray therefrom. However, the fixed opposing nozzles cannot be positioned to alter the direction of spraying of the refractory material. A separate operation is required by Haus to spray the bottom surface of the vessel, which requires tilting the entire apparatus. (Col. 4, 11. 62-67.) Tilting the apparatus is disadvantageous not only because it comprises an additional step and is per se difficult to accomplish, but also because effecting even spraying of the bottom of the vessel by such a technique is extremely difficult, as it requires the even application of the material through different degrees of tilt of the apparatus without any overlap of the sequentially applied layers of material.
Another disadvantage of Haus is that the discharge of refractory spray from the two nozzles precludes concentrating spray at only one particular defect point for specialized repair application purposes. For example, if one attempted to selectively spray a small defect located on one side wall of a refractory body with the Haus device, refractory spray would also be deposited on the side of the vessel opposite the defect, since the two nozzles of Haus simultaneously spray in opposite directions. This would cause an excess of material to be deposited on the opposite side of the vessel, which point would then be susceptible to chipping and faulting through to the underlying surface, thereby resulting in the creation of another defect as the result of the initial repair. Since defect points in a body therefore cannot effectively be repaired with the Haus apparatus, the interior surface may be susceptible to rapid deterioration.
Thus, there is a need in the art for a refractory spraying apparatus and method that can evenly spray all of the interior surfaces of refractory bodies, including deep-walled vessels. The device must be portable, usable in a vessel substantially above room temperature, and, in addition to having the capability of spraying all portions of the vessel evenly, must also have the capability of directing refractory material at a specific defect or fault point.